We have previously shown that populations of the fruit fly Drosophila melanogaster can learn in an olfactory discrimination paradigm. Using chemical mutagenesis and behavioral selection we have isolated four mutants which fail to learn in this test. Normal larvae can learn in a similar training situation. In contrast, larvae of the mutants above, like the adults are deficient in learning showing that the mutations are expressed early in development. Three of these mutants also fail in a different test, the leg-lifting paradigm previously developed by Horridge for cockroaches. We have isolated another mutant amnesiac, which learns normally but forgets rapidly after training. Amnesiac is apparently deficient in memory retrieval rather than storage. We are continuing the genetic mapping and developmental characterization of these mutants. We are also testing their capacity for elementary behavioral plasticity (i.e. habituation and sensitization). We are currently looking for anatomical abnormalities and we will screen for alterations in neurotransmitter levels correlated with genetically induced loss of learning ability.